In association with recent trend toward a larger screen size, a higher picture quality, and a higher quality, it is important that the picture size of a cathode-ray tube (CRT) television receiver be unchanged despite a change of a high voltage. A conventional vertical/horizontal amplitude control device for controlling a change of the picture size due to the change of the high voltage will be described.
FIG. 3 is a block diagram of the vertical/horizontal amplitude control device for controlling vertical and horizontal amplitudes based on the change of the high voltage. A video signal is converted into RGB signals in RGB processor block 31. Amplitudes of the signals are then controlled in gain control block 32, and the video signal is displayed on picture tube 33. A beam current that flows when displaying the video signal is detected as the change of the high voltage. The change of the high voltage is supplied to vertical amplitude control section 34 and horizontal amplitude control section 35. By controlling the vertical amplitude and the horizontal amplitude according to the change of the high voltage, a change of the picture size due to the high voltage change can be reduced. Vertical sawtooth-wave controller 36 controls a linearity of a vertical sawtooth wave and performs an S-character adjustment. Pin-cushion controller 37 performs a waveform control of a pin-cushion waveform.
Since the above sections control vertical and horizontal amplitudes after a beam current flows, that is, after the high voltage changes, the control device cannot correct the amplitudes appropriately because of a delay of control of the vertical and horizontal amplitudes after the change of the high voltage. This causes the change of the vertical and horizontal amplitudes not to be reduced due to the high voltage change.